blockLimPID

P, PI, PD, and PID controller with limited output, anti-windup compensation and setpoint weighting

Extends from Modelica.Blocks.Interfaces.SVcontrol (Single-Variable continuous controller).

Information

This model is similar to Modelica.Blocks.Continuous.LimPID, except for the following changes:

It can be configured to have a reverse action.

If the parameter reverseAction=false (the default), then u_m < u_s increases the controller output, otherwise the controller output is decreased. Thus,
- for a heating coil with a two-way valve, set reverseAction = false,
- for a cooling coils with a two-way valve, set reverseAction = true.
It can be configured to enable an input port that allows resetting the controller output. The controller output can be reset as follows:
- If reset = IBPSA.Types.Reset.Disabled, which is the default, then the controller output is never reset.
- If reset = IBPSA.Types.Reset.Parameter, then a boolean input signal trigger is enabled. Whenever the value of this input changes from false to true, the controller output is reset by setting y to the value of the parameter y_reset.
- If reset = IBPSA.Types.Reset.Input, then a boolean input signal trigger is enabled. Whenever the value of this input changes from false to true, the controller output is reset by setting y to the value of the input signal y_reset_in.
Note that this controller implements an integrator anti-windup. Therefore, for most applications, keeping the default setting of reset = IBPSA.Types.Reset.Disabled is sufficient. Examples where it may be beneficial to reset the controller output are situations where the equipment control input should continuously increase as the equipment is switched on, such as as a light dimmer that may slowly increase the luminance, or a variable speed drive of a motor that should continuously increase the speed.
The parameter limitsAtInit has been removed.
Some parameters assignments in the instances have been made final.

Parameters

Type	Name	Default	Description
Modelica.Blocks.Types.SimpleController	controllerType	Modelica.Blocks.Types.SimpleController.PID	Type of controller
Real	k	1	Gain of controller
Modelica.SIunits.Time	Ti	0.5	Time constant of Integrator block
Modelica.SIunits.Time	Td	0.1	Time constant of Derivative block
Real	yMax	1	Upper limit of output
Real	yMin	0	Lower limit of output
Real	wp	1	Set-point weight for Proportional block (0..1)
Real	wd	0	Set-point weight for Derivative block (0..1)
Real	Ni	0.9	Ni*Ti is time constant of anti-windup compensation
Real	Nd	10	The higher Nd, the more ideal the derivative block
Boolean	reverseAction	false	Set to true for throttling the water flow rate through a cooling coil controller
Initialization
Modelica.Blocks.Types.InitPID	initType	Modelica.Blocks.Types.InitPID.DoNotUse_InitialIntegratorState	Type of initialization (1: no init, 2: steady state, 3: initial state, 4: initial output)
Real	xi_start	0	Initial or guess value value for integrator output (= integrator state)
Real	xd_start	0	Initial or guess value for state of derivative block
Real	y_start	0	Initial value of output
Advanced
Boolean	strict	true	= true, if strict limits with noEvent(..)
Integrator reset
IBPSA.Types.Reset	reset	IBPSA.Types.Reset.Disabled	Type of controller output reset
Real	y_reset	xi_start	Value to which the controller output is reset if the boolean trigger has a rising edge, used if reset == IBPSA.Types.Reset.Parameter

Connectors

Type	Name	Description
RealInput	u_s (from SVcontrol)	Connector of setpoint input signal
RealInput	u_m (from SVcontrol)	Connector of measurement input signal
RealOutput	y (from SVcontrol)	Connector of actuator output signal
Modelica.Blocks.Interfaces.BooleanInput	trigger	Resets the controller output when trigger becomes true
Modelica.Blocks.Interfaces.RealInput	y_reset_in	Input signal for state to which integrator is reset, enabled if reset = IBPSA.Types.Reset.Input

Components

Type	Name	Default	Description
Real	controlError	u_s - u_m	Control error (set point - measurement)
Modelica.Blocks.Math.Add	addP		Adder for P gain
Modelica.Blocks.Math.Add	addD		Adder for D gain
Modelica.Blocks.Math.Gain	P		Proportional term
Utilities.Math.IntegratorWithReset	I		Integral term
Modelica.Blocks.Continuous.Derivative	D		Derivative term
Modelica.Blocks.Math.Add3	addPID		Adder for the gains

Revisions

September 29, 2016, by Michael Wetter:
Refactored model.
August 25, 2016, by Michael Wetter:
Removed parameter limitsAtInit because it was only propagated to the instance limiter, but this block no longer makes use of this parameter. This is a non-backward compatible change.
Revised implemenentation, added comments, made some parameter in the instances final.
July 18, 2016, by Philipp Mehrfeld:
Added integrator reset. This is for issue 494.
March 15, 2016, by Michael Wetter:
Changed the default value to strict=true in order to avoid events when the controller saturates. This is for issue 433.
February 24, 2010, by Michael Wetter:
First implementation.